The present invention relates to a developing device for an electrophotographic image forming apparatus, and a toner cartridge for replenishing a fresh toner to the developing device.
A copier, facsimile apparatus, laser printer or similar electrophotographic image forming apparatus has a developing device for developing a latent image electrostatically formed on a photoconductive element, or image carrier, by using a toner. It has been customary with this kind of apparatus to replenish a fresh toner into the developing device from a toner cartridge removably mounted to the developing device. The developing device includes a toner storing section or hopper for receiving the fresh toner from the cartridge. During the course of development, the toner is sequentially fed from the hopper to the photoconductive element. The toner consists of toner particles and an additive. The problem with the conventional developing device is that as the developing device is operated a number of times, the additive concentration of the toner increases. As a result, the toner density, i.e., the density of an image developed by the toner is lowered. Specifically, although the additive should ideally be transferred to the latent image of the photoconductive element together with the toner particles, the additive is, in practice, left in the hopper without being consumed. Moreover, assume that the developing device or the entire image forming apparatus is held in an inclined position by accident. Then, because the toner is fed over the entire length of the photoconductive element, the additive concentrates on one end portion lower in level than the other end portion. This further increases the additive concentration of the toner and thereby aggravates the decrease in toner density or image density.